Movement of the joints of human musculoskeletal system involves movements of adjacent bones through various ranges of motion. For example, movement of the human knee involves movements of the femur, tibia and the patella. Specifically, during flexion and extension, the distal end of the femur and the proximal end of the tibia articulate relative to one another through a series of complex movements as the patella articulates with the femur. Similarly, movement of the human hip involves movements of the femur with respect to the acetabulum, and movement of the shoulder involves movement of the humerus with respect to the glenoid. Damage (e.g., trauma) or disease can deteriorate the bones, articular cartilage, and ligaments of the bones associated with these joints, which can ultimately affect the ability of the natural joint to function properly. As a result, orthopaedic prostheses have been developed and implanted into surgically prepared ends of the bones of the joints to provide greater mobility for the patient.
For example, a typical orthopaedic prosthesis 10 for a total knee replacement is shown in FIGS. 1 and 2. The illustrated prosthesis includes a tibial component 12 or tibial tray to be coupled to the patient's proximal tibia, a femoral component 14 to be coupled to the patient's distal femur, and a bearing component (or tibial insert) 16 positioned between the tibial tray and the femoral component.
Once implanted, articular surfaces 18, 20 on the femoral component bear and articulate against articular surfaces 22, 24 on the proximal surface of the tibial insert 16 as the knee is moved through flexion and extension. A groove on the femoral component 14 provides a third articular surface 26 that articulates against a bearing surface on a patellar implant component (not shown) as the knee is flexed and extended. Other surfaces 26, 28 of the implants 12, 14 face the bone when implanted, and may have cement pockets or textured surfaces to encourage bone ingrowth.
A typical orthopaedic prosthesis 30 for hip replacement is shown in FIGS. 3-5. The hip prosthesis 30 includes a metal stem 32 and metal femoral head 34 and an acetabular implant assembly 36 including an acetabular cup 38 and a bearing component (acetabular liner) 40 fixed to the acetabular cup 38 and receiving the femoral head 34.
In the embodiment illustrated in FIG. 4, the stem 32A has some differences compares to the stem 32 of FIG. 3. In both, the femoral implant is modular, comprising an assembly of a stem 32 or 32A component with a femoral head component 34. The head component 34 defines a curved articular surface 42 that is received within and articulates against a concave articular surface 44 of the acetabular liner 40. The majority of the length of the stem 32 defines a bone-facing surface 46 extending proximally from the distal end 47 bears against and faces the bone (proximal femur). The exterior surface of the cup 38 also defines a bone-facing surface 48.
A typical orthopaedic prosthesis 50 for shoulder replacement is illustrated in FIG. 6. includes a metal stem 52 and metal humeral head 54 and a glenoid component 56. Common glenoid components 56 include a metal portions and a bearing 58 fixed to the metal portion and receiving or articulating against the humeral head 54. The head component 54 defines a convex curved articular surface 60 that is received within and articulates against a concave curved articular surface 62 of the bearing 58. The majority of the length of the stem 52 defines a bone-facing surface 64 extending proximally from the distal end 66 and bears against and faces the bone (proximal humerus). The exterior surface of the glenoid component also defines a bone-facing surface. FIG. 6 illustrates the shoulder prosthesis 50 implanted in the proximal humerus and glenoid.
In such typical orthopaedic prostheses, the tibial tray 12, distal femoral component 14, femoral stem 32, femoral head 34, acetabular cup 38, humeral stem 52, humeral head 54 and part of the glenoid component 56 are typically made of metal, such as a cobalt chrome alloy or a titanium alloy (such as titanium alloy Ti-6Al-4V, for example). The bearing component (tibial insert 16, acetabular liner 40 or glenoid bearing 58) is typically made of a polymer, or in the case of hip prostheses, may comprise a metal or ceramic liner. In some cases, the entire tibial component and entire glenoid component may comprise a polymer.
The polymer used for the bearing components 16, 40, 58 may be ultrahigh molecular weight polyethylene (UHMWPE). The UHMWPE may comprise a cross-linked material, for example. Techniques for crosslinking, quenching, or otherwise preparing UHMWPE are described in numerous issued U.S. patents, examples of which include: U.S. Pat. No. 5,728,748 (and its counterparts) issued to Sun, et al.; U.S. Pat. No. 5,879,400 issued to Merrill et al.; U.S. Pat. No. 6,017,975 issued to Saum, et al.; U.S. Pat. No. 6,242,507 issued to Saum et al.; U.S. Pat. No. 6,316,158 issued to Saum et al.; U.S. Pat. No. 6,228,900 issued to Shen et al.; U.S. Pat. No. 6,245,276 issued to McNulty et al.; and U.S. Pat. No. 6,281,264 issued to Salovey et al. The disclosure of each of these U.S. patents is incorporated by reference herein in their entireties. The UHMWPE of the bearing material may be treated to stabilize any free radicals present therein, such as through the addition of an antioxidant such as vitamin E. Techniques for stabilizing UHMWPE with antioxidants are disclosed, for example, in U.S. Pat. Pub. No. 20070293647A1 (Ser. No. 11/805,867) and U.S. Pat. Pub. No. 20030212161A1 (Ser. No. 10/258,762), both entitled “Oxidation-Resistant And Wear-Resistant Polyethylenes For Human Joint Replacements And Methods For Making Them.”
Each of these implant systems share some common characteristics: an articulation surface 18, 20, 26, 42, 60 of one implant component 14, 34, 54 (usually metal or ceramic) bears and articulates against an articular surface 22, 24, 44, 62 of a bearing component 16, 40, 56. Over years of repeated use, the repeated articulation of these components against one another can lead to wear of the bearing component 16, 40, 56. Excessive wear of the bearing component can lead to issues requiring that the prosthetic joint be removed and replaced with another prosthetic implant in a revision procedure.
To address wear, various solutions have been proposed. For example, attempts have been made to reduce wear by optimizing the polishing of the metal articulating surface(s) to a high gloss. Such polishing processes can however be costly. Some have suggested providing a textured surface through etching or anodizing to contain a biological fluid to improve lubrication. See, for example, WO2015/034471A1.